Chemical sensitization of photographic emulsions



Patented Sept. 12, 1950 GHEMIGALLSEN SITIZAIIDNI'QE "PHOTO?- GRABHIG EMUDSIONS Wesley G. Lowe and' Charlesxll.lHivAllcm-Ronhaester, N. Y., assignors to EEStlllfl-ILKDfiflkiQOlflw pany," Rochester, N; Y., azcorporatione oflNew- Jersey.

No Drawing. ApnlicatiomNhvemhewlS} 71948-3 SerialTfNc. 60,815

101 Claims;

invention relates tophotographic emulsionsandmo-re particularly to chemical sensitiz= ers therefor.

It" is well known that silver" halideemulsions maybechemically sensitized with a variety oft materialsso' as to increase the speed and" gener ally-the-gamma of the emulsions as opposed to optical sensitizing in which the opticalrange of sensitivity, is increased. Depending uponthe materials-andlmethod's employed; it*' is generally regarded that chemical sensitization results in either the:formation' ofsilver sulfid'e n the-surfaces of thezsilver' halide" crystal or" results in the formation of small amounts" of silverfrom the reduction, of" silver halide; whicheiiect" may be il'liBJdditiOE-FIO theiormereffect sometimesknown as sulfur" sensitizing: The presentinvention is concerned primarily" with chemical sensitization apparently'of *the' latter type;

Among the materials previously proposed-for augmenting emulsion sensitivity may;- be' mentioned" basic compounds" such' as ammonia and certain aromatic and? aliphatic-i amines such as" trieth'ylamine and-1 triethanolamine; whereas other amines such as propylamylhexy-lamine" are said to have no effectupon emulsion sensitivity: Similarly, we havefound that' simple polyamines such"as, ethylenediamine arenot'effectivechemi cal sensitizers' for" silver halide emulsions: On the other hand; we" have discovered a certainpolyamine" compound similarini structure to ethylene diamine which surprisinglyisa" powerful sensitizer for silverhalide emulsions:

One'objectofour invention is-toprovidechemicallysensitized silver halide emulsions of en'- hanced sensitivity. Another: obj ecttis' to provide a novel' chemical sensitizing agent" for" photographic. emulsions". Another" objectis to provide photographic emulsions havingthe sensitivity enhanced "by means of 'both sulfur'sensitizersand the novel sensitizer, of our'invention. A further objectis tofprovidethe methods of augmenting emulsionzsensitivity utilizing the novel sensitizing'agent; Another object is to provide photo.- graphic: elements ini which the novel emulsions are useful. Further objects of ourginventionwill become apparent from consideration of the fol lowing; description.

The objectslofiourr invention are accomplished in par-thythe'incorporation in silver halide emulsionlayers of'a polyaminecompound of the structure such as spermi'ner. Spermine has the formula I-IzNlCI-Iz) 3NH CHMNH CH 'sNHv and is representative of polyamines having both propylene and butylene groups separated by nitrogenlatoms. In additiorrtowthe polyaminemene tinned; 4 we" find equally useful for incorporation in emulsions the'water -soluble-sa=lts= of'thaamine with acids-- having a non-desensitizingeffect on emulsions suchasthe acetates; carbonates, sulfates andhydrochloridesalts;

Thenovel sensitizeris incorporated in emulsions-at any-stage-in their preparation but preferably before digestionis complete. Generally,

in. orderto obtain theoptimum sensitizing,effect,v

we heat the emulsion afteraddition of; the sensi-- tizingra fintn Thesensitizers may be, used inconjunction.v with. other, chemical I and optical sensitizers-lsuchs as. the -,well;known sulfur sensitizing compounds such ,as disclosed; in- Sheppard; U) S, Batentsx 1,534,944.. granted; March. 2,, 1,926; and 1,623,499} gitantedL,ApriI;5',-. 1i927. Ourgnovel. sensitizerlmayice-employed before, after orlsimultanee ously withsulfiir, sensitizing',,. Also our novel. sen:- sitizer is useful with ,arvariety of emulsionapro: ducing pronouncecllspeed increases. in either negativecor nositiVetypesof emulsions.

Ojun invention will .now. be illustratedby reference. to: the; following, specific, examples Examplcdr cc: samples of ahigh speed bromoiodide negative" type ofemulsion containingsilve halide from-26*grams"of'silver nitrate and 32 grams of gelatin were eaclrdiluted" with water; to- 460- cc; and thepH adjusted' to 6.4; To-on'esample of emulsionwas added-0J5 mg; ofspermine inaque 0'LlSSO1l,lti0Il adjustedto pH 7.0 with aceticacid. Thisemulsion and the control sample wereheatecl for45minut'es-at159' CL, coo1edto*40; andeach sample further sensitized.- by heating at 59 C. with asulfur? sensitizing agent. such as". disclosed inthe sheppard patents abovee; g; Allylthiourea', until test" indicated thatmaximum speed; had beerrreached. Aiter'coating and drying the sampies as -usual, exposurein anEastrrian: Type 112' sensitometerlJ." PI E. 17' (1931)'p. 536) and deve-loping'4*min1 in the following'developer; the coatings had the characteristics shown. in the tabletfollowing' (samples A' andB) dide emulsion, each containing silver halide obtained from 20 grams of silver nitrate and peptized with a gelatin derivative by the process of the Lowe et a1. U. S. application Serial No. 768,-

478, filed August 13, 1947, were adjusted to pH 6.0. To one sample was added 4 mg. of spermine in aqueous solution adjusted to pH 6.0, and both samples were then heated for 30 minutes at 50 C. After coating and drying the samples asusual', exposure was made on the 1b sensitometer and development carried out in the following developer.

The exposed and processed samples were found to have the characteristics shown in the above table (samples C and D).

It will be apparent from consideration of the above data that spermine is effective in producing large speed increases in emulsions treated therewith, in most cases the increases with sulfur sensitized emulsions being considerably greater than expected from the activity of the individual sensitizers when used alone. However, the speed increases obtained in absence of sulfur sensitizing are appreciable and valuable.

In the manner of the above examples, other types of silver halide emulsions may be treated with our novel sensitizing agent alone or in conjunction with other chemical or optical sensitizers. The amount-of sensitizing agent may, depending upon the type of emulsion used, vary somewhat from the optimum amounts employed in the above examples, one-fifth to five times as much sensitizin agent producing emulsions of useful sensitivity. As is apparent, less heating is usually required when the larger amounts are employed and conversely when using the smaller quantities of sensitizin agent.

It will be noted in the above examples that the sensitizing of the emulsions with the novel compound was eifected at relatively low pH- This is not a limitation of our invention but more an advantage thereof since we are able to suppress sulfur sensitivity by lowering the pH of the emulsion and since the novel sensitizer is so active, further sensitization takes place even substantially below tate and co-polymers of polyvinyl alcohol. The

ratio of colloid to silver halide present during the digestion is not critical in this type of sensitizing since the digestion conditions can be readily adjusted as is well known in the: art of sulfur sensitizing. The sensitizers are suitable for the well known typesof silver chloride, silver bromide and silver iodide emulsions and emulsions containing mixtures of these halides, containing the usual emulsion addenda such as antifoggants, spreadin agents, coupler compounds, etc. 5 Such emulsions are suitable to use in forming single as well as multilayer film useful in color photography which customarily include two or more emulsion layers on a support sensitized to difierent regions of the visible spectrum andmay. or may not contain coupler compounds;- Accordingito Tour invention such color films carry at least one emulsion layer containing a sensitizing agent of our invention.

Our inventionhaving been described, We would have it understood that the preceding description is by way of example only and that our invention is to be taken as limited only by the scope of the appended claims.

What we claim is:

l. A light-sensitive photographic emulsion comprising silver halide and a polyamine sensitizing agent selected from the group consisting of spermine and its water-soluble salts of non-desensitizing acids.

2. A light-sensitive photographic emulsion comprising silver-halide and spermine as a sensitizing agent.

3. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and as an additional sensitizing agent a sensitizing agent selected from the group consisting of spermine and its water-soluble salts of non-desensitizing acids.

.4. A li ht-sensitive photographic emulsion comprising sulfur sensitized silver halide and spermine as an additional sensitizing agent.

5. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion and eifecting a further increase in sensitivity by treatment of said emulsion with a sensitizing agent selected from the group consisting of spermine and its water-soluble salts of non-desensitizing acids.

4 tivity by treatment of said emulsion with spermine.

p 7. The method of sensitizin a photographic silverehalide emulsion which comprises digesting said emulsion in the presence of a sulfur sensitizing agent and a sensitizing agent selected from the group consisting of spermine and its water-soluble salts of non-desensitizing acids.

8. The method of sensitizing a photographic silver halide emulsion which comprises digesting said emulsion in the presence of a sulfur sensitizing agent and spermine.

9. The method of sensitizing a photographic silver halide emulsion which comprises imparting sulfur sensitizing to said emulsion, adjusting the the neutral point when it is added to the emulsion. pH of Sam emulslon to below neutrahty and further sensitizing said emulsion by digestion of said emulsion in the presence of spermine and its water-soluble saltsof non-desensitizing acids.

10. The method of sensitizing a photographic silver halide emulsion which comprises imparting sulfur sensitizing to said emulsion, adjusting the pH of said emulsion to below neutrality and further sensitizing said emulsion by digestion of said emulsion in the presence of spermine.

WESLEY, G. LOWE. CHARLES F. H. ALLEN.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSION COMPRISING SILVER HALIDE AND A POLYAMINE SENSTIZING AGENT SELECTED FROM THE GROUP CONSISTING OF SPERMINE AND ITS WATER-SOLUBLE SALTS OF NON-DESENSITIZING ACIDS. 